1. Field of the Invention
The present invention relates generally to electrical outlet boxes and the like and relates more particularly to certain new and useful improvements in the configuration and structure of the cable entry ports in such boxes which facilitate the admission of electrical power cable into the outlet box and retention of the installed cable in the box.
The usual electrical outlet box is constructed in a generally open top, box-like configuration with a generally continuous side wall member depending from a back or bottom wall, and formed with one or more cable entry ports (hereinafter sometimes referred to as "knockout windows") in the side wall member, which are adapted to permit access of electrical power cables into the interior of the box. One or more electrical power cables are inserted into the box, each through a cable port opening, for connection of the conductor wires to, or termination with, the electrical fixture to be mounted in the box. Moreover, in order to prevent debris from entering the box through cable ports that are not utilized, and to minimize fire spead in the event that the electrical appliance housed in the box malfunctions, the typical cable entry ports in electrical outlet boxes are substantially completely closed by "knockout" panels which are removably attached to the box wall structure across each port opening.
It will be understood that although the present invention is described with particular reference to electrical outlet boxes which are adapted to house the termination, i.e., electrical connection, between the conductor wires of an electrical power cable and an electrical fixture such as an electrical outlet receptacle or an electrical switch, the present invention may be adapted, where desired, for use in other housings for electrical distribution appliances, such as electrical junction boxes, flush type boxes, etc. Accordingly, when used herein, the term "electrical outlet box" is intended to embrace such additional structures.
Also, although the present invention is described with particular reference to an electrical outlet box formed from a moldable plastic material and to insulated electrical power cable having an oval jacket of a molded plastic composition which is soft and readily deformable, known in the art as "ROMEX" cable, the present invention may be adapted for use in an electrical outlet box formed from a metallic material, in which case it will be understood that either the aforesaid "ROMEX" cable or the helical metal jacketed cable, known in the art as "BX" cable, may be used. Accordingly, the term "electrical power cable" is intended to embrace both plastic and metal jacketed cables.
It will also be understood that although the present invention is described with respect to rectangularly-shaped electrical outlet boxes, the invention is equally applicable to other conventionally shaped boxes, including round boxes.
2. Description of the Prior Art
It is conventional for electrical outlet boxes to have a number of cable entry ports in which a panel or closure member normally substantially closes the port aperture and is removed, or "knocked-out", to permit passage of electrical power cable into the box.
As previously known, however, electrical outlet box "knockouts" have been disadvantageous from several standpoints. Thus, removal or deflection of the "knockout" from the port has heretofore required the use of a separate tool, such as a screwdriver or hammer or the like, resulting in a time-consuming two-step operation in order to insert the cable into the box. Also heretofore, the port aperture and the closure panel have been of a single fixed size, usually to accommodate the largest size standard electrical power cable possible under the applicable electrical code regulations, such that, upon removal of the closure panel, there is a substantial gap between smaller-sized standard power cables and the rim of the aperture, which subjects the installation to the aforementioned hazards of debris collection and fire spread.
In some applications, it also has been found that the connection between the conductor wires of the cable and the electrical appliance may be stressed or dangerously loosened by forces exerted on the cable or wires at other locations after installation. In addition, during construction of the wall structure in which the outlet box is installed, the cable conventionally is inserted through the cable entry port after the box is mounted in place, but the electrical appliance may not be connected to the cable and installed in the outlet box until after the wall structure is secured in place. The cable is thereby susceptible to accidental removal from the cable entry port before it is connected to the appliance, and a significant, further time-consuming effort may be required to reinsert the cable into the box.
In order to fixedly retain the cable in the box for preventing such stressing on the connections or for preventing removal from the knockout window, clamping devices have been previously developed or proposed, which are adapted to be secured in or adjacent each knockout window opening and to grasp the cable firmly for preventing withdrawal from the box. In fact, such clamping devices are presently required by the National Electric Code for multigang boxes and for so-called "old work" boxes.
Heretofore, however, most cable clamping devices have been formed as independent structures which have to be fabricated separately from the box itself, in relatively complicated structures, such as shown in U.S. Pat. Nos. 3,788,582 issued to Swanquist, and 3,493,205 issued to Bromberg. These structures involve substantial fabrication costs over and above those of making the box alone. In addition, since clamping devices have to be affixed to the box, they also entail additional installation time and consequent labor expense. Moreover, in order to be fixedly secured in the knockout window of the box, the engaging means for the separate clamping device must be proportioned to fit the particular configuration of the knockout window. Thus, unless all knockout window apertures are standardized in size and shape, numerous different sized and/or shaped devices are needed, thereby greatly increasing the costs of manufacture, inventory and installation time.
Although a metal electrical outlet box has been proposed in which a cable clamp is formed integrally with the box structure, such as U.S. Pat. No. 3,112,938 issued to I. P. Karlin in 1963, the clamping structure there proposed does not automatically grasp nor resistingly bear against the installed cable and several manipulative steps with separate tools are necessary in order to assemble the cable port closure structure into a clamping position. Thus, the Karlin structure is not self-opening nor self-clamping nor self-adjusting. Moreover, the Karlin U.S. Pat. No. 3,112,938 structure is disadvantageous since it is possible to erect Karlin's port structure with too large of a space between the cable engaging edge of the port structure and the cable, so that clamping either is not effected at all or necessitates more manipulation to establish the proper spacing in order to obtain a clamping action.
A thermoplastic electrical junction box with an integral locking and sealing structure also has been proposed in Swiss Pat. No. 349,319 issued to F. Meili in 1960. In that patent, the entry ports of the box are normally closed by knockout or cut-out covers which, when removed in the conventional manner, leave a circular rim of slightly smaller diameter than that of the port aperture, which is inclined inwardly of the aperture to form a relatively rigid and relatively sharp circular inner edge. Thermoplastic insulating pipe for carrying electrical conductor wires is formed with transverse cuts in the surface thereof and then inserted into the box aperture, whereupon the aforesaid relatively sharp inner edge of the aperture rim enters the cut in the manner of a barb to both seal and lock the pipe within the aperture against reverse outward movement. As in the Karlin U.S. Pat. No. 3,113,938, the 1960 Swiss Pat. No. 349,319 is therefore not self-opening and is not self-clamping as the structure does not automatically grasp nor deflect laterally so as to resistingly bear against the installed pipe. The Swiss patent's entry port structure is also not self-adjusting to different sizes of pipe and is otherwise disadvantageous since the requirement for cuts in the surface of the installed pipe would be difficult to obtain in conventional metal jacketed cable and unacceptable in conventional insulated plastic jacketed cable.
Finally, Swiss Pat. No. 459,323 issued to A. Grossauer in 1968 discloses an injection-molded plastic electrical junction box having entry ports for electrical conduit piping which include relatively thin tongues molded integrally with the box, which are spaced radially about the rim of the entry aperture and extend in the plane of the aperture. The entire box is covered with a sheath of rubber or plastic, including the entry ports. Although this patent indicates that the tongues clamp tightly against the conduit piping when the latter is attempted to be withdrawn, the tongues are said to be relatively thin and are formed in the plane of the aperture and therefore very little clamping strength is available due to the large amount of deflection required to pass a conduit through the aperture. Also, due to their location and orientation in the plane of the aperture, it is believed that the tongues would be easily broken upon application of a reverse outward force on the conduit and, at best, only a small range of different-sized cables could be accommodated by any one length of tongue. Also, the provision of a rubber or plastic sheath enveloping the entire box in order to close the conduit entry ports is believed to be impractical and tends to disguise their location, making installation of the conduit more difficult.